1. Field of the Invention
This invention generally relates to a system for forming images, such as printers, copiers and facsimiles, and in particular to an image forming system including an image forming main unit and one or more optional units operatively coupled to the main unit for forming an image in the form of a hard copy based on image information produced internally or received from an external system. In particular, the present invention relates to an image forming system in which various items of information relating to formation of an image are exchanged between the main unit and one or more of the optional units before formation of an image in the form of a hard copy.
2. Description of the Prior Art
An image forming system, such as a printer system, is being diversified in function. For this purpose, the modern image forming system has a modular type structure which includes a main unit and one or more optional or auxiliary units operatively coupled to the main unit. For example, the main unit may include a laser beam printer and the optional units may include such units as large volume paper feeding units, large volume paper discharging units, mail boxes, sorters, both side or duplex imaging units and automatic document feeders. Such a system is highly desirable because it is flexible in structure, and any desired and unique image forming architecture can be constructed by the user by selecting one or more desired optional units to be operatively coupled to the main unit.
Such an image forming system, highly flexible and responsive to the needs and demands of the user in structure, but still had disadvantages, perhaps because it is relatively new in idea. For example, since a complete image forming system is constructed by selecting one or more optional units to be connected to the main unit, there must be provided a communication path between the main unit and the selected optional units and various items of information relating to image formation must be exchanged between the main and optional units. It is a customary practice to use a multi-line connection code between the main and optional units via multi-terminal connectors so as to allow for the exchange information in a parallel communication mode. However, in such a case, as the system is expanded with addition of more optional units, there must be provided an increased number of multi-terminal connectors, some identical and some different in structure and multi-line connection codes, which is disadvantageous in many respects. For example, connections between the main and optional units become complicated and expensive, so that there is a possibility of establishing erroneous connections and skill and experience are required to establish correct connections.